Many convertible vehicles are provided with roll bars or hoops for protecting the driver and passengers in the event of the vehicle overturning. Some roll bars currently found on motor vehicles are fixed in position and some are stowed in a retracted position out of sight and deployed when required.
GB-A-157543 discloses a deployable roll bar which pivots from a horizontal stowed position to a vertical deployed position. The roll bar is located behind the front seat of a vehicle and is triggered by means of a pyrotechnic device in conjunction with a sensor responsive to vehicle rotational acceleration or angle of rotation.
U.S. Pat. No. 5,458,396 discloses a deployable u-shaped roll bar that is stowed in a retracted position in the headrest or backrest of a seat and which extends upwards above an occupant's head in a deployed position. The roll bar's deployment system includes a spring-loaded release member and a hold member so that on deployment, the roll bar may be forced upwards by the action of the spring and locked in an extended position by the hold member.
GB-A-2,184,586 discloses sensor means for controlling deployment of a roll bar. A first sensor comprises an inertia switch located centrally in the vehicle and a second sensor means comprises switches located on the rear wheels of the vehicle, each switch being closed when the rear wheel suspension is completely extended, and a third sensor comprising a tilt switch. This combination of switches facilitates deployment of the roll bar when overturning of the vehicle is imminent and inhibits deployment when the vehicle is lifted in a workshop or is driven over a hump.
When designing either fixed or deployable roll bar arrangements for motor vehicles, certain constraints have to be taken into account.
Firstly packaging constraints must be considered, so that the roll bar can be located in the vehicle optimally.
Additionally for protection, the static or deployed position has to be sufficiently high in order to offer a protective ‘zone’ in which the occupants are retained, thus avoiding or minimising contact between an occupant's head and the road surface when the vehicle is rolling or static on the ground.
Further, there must be allowance for the operation of a roof-folding mechanism and the travel envelope when folding or unfolding the roof.
Deployable roll bars must be able to reach a point where protection is afforded irrespective of the position of the roof, i.e. up or down.
Known roll bar arrangements meet the above constraints by virtue of roof design. That is, the roof is positioned so that it clears the roll bar in its deployed condition, thus allowing the roll bar to function in either case of roof position, up or down. This has led to a compromise on the styling, aerodynamics and other factors related to the roof design, this being undesirable from a marketing and competitive point of view.
Thus there is a need for a deployable roll bar which will operate within the constraints mentioned above and which will allow design freedom with regard to the overall appearance of the vehicle, particularly the roof-line, the size and location of the rear window and the possibility of utilising glass as the material for the rear window.